Saturday, September 6, 2008

Landscape, Nursery, Turf, and Greenhouse - Water Absorbing Polymers II

The following is more information on water absorbing polymer use in horticultural applications during establishment.

Hydrogels have been used in field establishment of revegetation projects, as well as perennial, and annual establishment and production. Plants installed in media with hydrogels have had different responses. For instance, plants requiring more moisture than is readily available seem to benefit from hydrogel additions, but negative responses can occur if the hydrogels are used in environments that are naturally moist and xeriphytic plants are planted. Plants also have unique responses for different growth stages, so amounts of hydrogel required may vary as a plant develops.

Research on plant establishment in dry conditions has shown benefits for using these hydrogels (water absorbing polymers). Pinus halepensis (Aleppo pine) doubled its survival rates in 0.4% hydrogel soil compared to no hydrogel amendments. The hydrogel also prolonged water availability for plant use when irrigation was stopped. The hydrogel media also allowed for 19 days to pass before plants started to die whereas in the control with no hydrogel plants started to die after five days of drought. Pinus pinea (umbrella pine or Italian stone pine) seedlings survived 1.4 to 2.0 times longer with applications of hydrogels compared to the trials with no hydrogels in the field production. Pinus halepensis also had increased adventicous root growth along with increased overall plant mass when the hydrogel was added to the media. Research has shown that Quercus rubra (red oak) and Nyssa sylvatica (black gum) had increased root regeneration when rooting hormones were added to the polymers for transplant aids. Dehgan and others (1994) noted that foliage plants like Photinia x fraseri (Fraser photinia) responded in increased mass to the incorporation of hydrogels into media.

Hydrogels usually have some effect on plant establishment, with the greatest benefit for moisture loving plants planted in dryer conditions. Festuca arundinacea ‘Rebel’ (Tall fescue) benefited from pre-seeding incorporation of hydrophilic polymers into the soil. Pyracantha cocinnea (scarlet firehorn) and Rhododendron sp. (azalea) had increased survival and increased dry weights in container production when a hydrogel was incorporated into the media. Drought sensitive annuals, such as Petunia parviflora (petunia), responded well to hydrogels in dry conditions and increased flower numbers and dry weights.

Not all plants respond the same to hydrogels. One issue is that thay retain fertilizer salts. This can actually reduce plant growth. In container production of Betula pendula (European birch), hydrogel incorporation into the media has shown a reduction in overall plant mass and also decreased the amount of water available to the plants. After further investigation, the lack of water availability was attributed to the amounts of soluble salts in the media. Another research project found that Codiaeum variegatum (croton), Dieffenbachia sp. (dumb cane) and Hibiscus rosa-sinensis (hibiscus) showed no visible size differences when hydrogels were used compared to not being used. Annuals requiring dry regimes such as Catharanthus roseus (vinca) do not respond well to extra water being held by the soil.

Extracted from "Hydrophilic Polymers – Effects and Uses in the Landscape" by Daniel Peterson in the Restoration and Reclamation Review Student On-Line Journal, University of Minnesota, St. Paul, Minnesota (USA), Department of Horticultural Science

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